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Can someone please help me with the following code. My temp array of Point2D's never overwrite the previous one when the for loop execute again.

I used for-loops to print data in order to test if temp array does change...and it certainly don't... Why would something like this happen?

Point2D is defined in a different class. It's x, y and z values are public.

I think it may be the .clone() function?

Thanks!

Point2D[] pointArr;
pointArr = populateArr(N);  

    for (int i = 0; i < N; i++)
    {
        Point2D[] temp = pointArr.clone();

        if (i >= 0) 
        { 
            Point2D exch = temp[i]; 
            temp[i] = temp[0]; 
            temp[0] = exch;
        //temp[0].z = 0.0;
        }

        System.out.println();

        temp = determine_slopes(temp, N);

        Arrays.sort(temp, temp[0].X_ORDER);

    }

EDIT 1: Just to clarify... I actually WANT the Point2D[] temp to change with each iteration... But for some reason it doesn't change. What may be the problem?

EDIT 2: My output for pointArr is as follow:

10000 0 0.0 0 10000 0.0 3000 7000 0.0 7000 3000 0.0 20000 21000 0.0 3000 4000 0.0 14000 15000 0.0 6000 7000 0.0

When I print I print the temp after the first Iteration my ouput does not look like pointArr's... It's totally different.

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3 Answers

up vote 2 down vote

This line should be outside the for loop

Point2D[] temp = pointArr.clone();
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up vote 4 down vote

The array declaration should be moved outside of the loop. Else you will create a new instance of the array each iteration of the loop, overwriting the previous one:

Point2D[] pointArr;
pointArr = populateArr(N);
Point2D[] temp = pointArr.clone();  //move to here

    for (int i = 0; i < N; i++)
    {


        if (i >= 0) 
        { 
            Point2D exch = temp[i]; 
            temp[i] = temp[0]; 
            temp[0] = exch;
        //temp[0].z = 0.0;
        }

        System.out.println();

        temp = determine_slopes(temp, N);

        Arrays.sort(temp, temp[0].X_ORDER);

    }

Edit: Im not sure this will help, but try creating a the copy of pointArr using a loop instead of clone:

Point2D[] pointArr;
pointArr = populateArr(N);
Point2D[] temp;

for(int i=0; i<pointArr.length; i++)
    pointArr[i]=temp[i];

If you, as you say, for some reason want temp to be overwritten, move the loop etc(that copy the array) inside your loop

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Thanks for the help! I actually want the temp array to be overwritten... Each iteration of the loop I want a new array that's exactly like pointArr. I changed my code, but it still doesn't overwrite the temp[] – ISJ Mar 15 '12 at 15:24
Basically I want the same pointArr for each iteration... – ISJ Mar 15 '12 at 15:27
Well, you are creating a clone of pointArr with temp each iteration. This means that it will contain the same elements as pointArr. So, you are creating a new array each iteration, that's a copy of pointArr, and since pointArr never change temp will look the same each time it's created. Im not sure what you're trying to achive here :) – John Snow Mar 15 '12 at 15:31
That's exactly what I try to achieve, but it's not working... For some reason the temp does not change... – ISJ Mar 15 '12 at 15:33
Well, temp does not change since it's a copy of pointArr, and pointArr never change. Try adding something to pointArr each iteration, and that will be added to temp aswell – John Snow Mar 15 '12 at 15:35
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up vote 1 down vote

I think your issue is that every time you loop through, you are re-setting your temp array to the pointArr clone. That's why when you exchange the values, it is lost every time b/c you are changing it in your temp array, but then setting temp array to the clone every time. Try declaring your temp array out of the for loop.

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